1. Field of the Invention
This present invention pertains generally to commercial ovens. More particularly, the present invention relates to systems for maintaining alignment of conveyor belts. The present invention is particularly, but not exclusively, useful for maintaining alignment of an oven conveyer, evenly on its rollers.
2. Description of the Related Art
Large commercial ovens used for baking food items, such as tortillas, typically employ conveyors to progress items within the oven during the baking process. A conveyor is typically comprised of an endless belt mounted on a series of rollers, with one roller driving the belt while the other rollers guide the belt and maintain its alignment. The tension in the belt must be maintained because the roller, which drives the conveyor, is usually friction driven; that is, the only force operating on the belt is the friction generated by the tension of the belt on the roller. The belts are often times a wire mesh construction, which is flexible enough to withstand the temperatures and stresses generated in the oven during operation. The belts are usually wide enough for and are designed to transport multiple rows of food items and maintain the items in rows to preserve the necessary spacing often needed for baking applications.
Many factors such as uneven loading or misaligned components can cause conveyor belts to wander in a transverse direction relative to the center of a roller. Particular to oven conveyors, uneven heat distribution is problematic to alignment of the belt. That is, uneven expansion of the wire mesh belt caused by a temperature gradient will cause the belt to drift out of alignment. An oven may contain several compartments with doors and opening a particular door will cause a heat imbalance to the belt. Also, commercial ovens are typically partially exposed to the ambient environment surrounding the oven. Changing air flow within the ambient environment can cause a heat sensitive belt to become misaligned. Empirically, belts have been observed to move in a transverse direction, toward the region of higher temperature. In theory, a higher temperature will yield more elasticity in that particular side of the belt, and therefore result in decreased tension in the side of the belt. According, a means to increase tension in that case would be necessary to correct alignment.
The problems associated with continuous misalignment of an oven conveyor can be very significant. First, the belt could severely damage the inside walls of the oven. Second, replacement of prematurely worn or damaged belts is a relatively expensive procedure both in actual cost and opportunity cost. The belts themselves are expensive at a cost of approximately $2,500.00 each. The man hours required for replacement is an additional cost. Furthermore, the entire oven must be shut down and cooled down, and therefore not producing volume during down time. In practice, maintaining proper alignment of oven conveyors extends belt life from 8 months to 18 months.
Existing oven conveyor alignment systems need improvement. One such system relies on mechanical switches that are intended to trip when a conveyor belt moves out of alignment. The mechanical switches, though, cannot continuously withstand the harsh environment inside an oven. Also, mechanical alignment systems are not reliable by today's standards, since they can frequently drift out of calibration. Thus, the mechanical alignment system will not be particularly suitable for making fine adjustments in alignment. Providing fine adjustments in alignment is preferred over complete shut down of the conveyor. Shut down while hot is additionally undesirable, and if required, a shut down preceded by a cool down process is preferred.
In light of the above, it is an object of the present invention to provide a system for aligning a conveyor that can accurately sense when a conveyor belt becomes misaligned. Another object of the present invention is to provide a system for aligning a conveyor belt that is capable of making fine adjustments, as required to maintain belt alignment. Yet another object of the present invention is to provide a conveyor belt alignment system that is capable of automatic control without operator intervention. Yet another object of the present invention is to provide a system for maintaining alignment in a conveyor that is simple to use, relatively easy to implement and superior to other designs known in the art.